Aggregation of at most five carriers is supported in the Long Term Evolution (LTE) Release 10 (Rel-10) carrier aggregation technologies. An eNB semi-statically configures component carriers to be aggregated for respective User Equipments (UEs). The configured component carriers are further categorized into active carriers and inactive carriers, and the eNB schedules data transmission only over the active carriers. The eNB activates and deactivates the configured carriers in a Media Access Control (MAC) Control Element (CE). If a UE determines the total amount of Acknowledgement (ACK)/Non-Acknowledgement (NACK) feedback information according to the number of active carriers, then the eNB may have different understanding of the total amount of ACK/NACK feedback information from the UE while the carriers are being activated and deactivated, and thus may fail to receive the ACK/NACK feedback information correctly. Accordingly the UE always determines the length of a sequence of feedback information according to the number of configured component carriers as specified in the LTE Rel-10. As illustrated in FIG. 1, the eNB configures the UE with three component carriers including DL CC1, DL CC2, and DL CC3, activates two of them, including the carrier DL CC1 and the carrier DL CC2, and schedules data transmission in the carrier DL CC1 in some sub-frame; and if a Multiple Input Multiple Output (MIMO) transmission mode is configured, and at most two Transport Blocks (TBs) are transmitted over each Physical Downlink Shared Channel (PDSCH), then the length of a sequence of ACK/NACK feedback information to be transmitted by the UE to the eNB may be 6, where feedback information corresponding to the active carrier DL CC2 which is not scheduled, and the inactive carrier DL CC3 is set to NACK.
Aggregation of at most 32 carriers is supported in the LTE Release 13 (Rel-13) carrier aggregation technologies. As there are a growing number of carriers to be aggregated, the UE will also transmit a significantly growing amount of ACK/NACK feedback information. If the length of a sequence of feedback information is still determined according to the number of configured carriers, then if the eNB configures the UE with a large number of component carriers, but there are a small number of component carriers which are really activated or scheduled, then there will be a large amount of redundant information in the sequence of ACK/NACK feedback information. The UE has to transmit a large amount of ACK/NACK feedback information over more physical resources and at higher transmit power, thus degrading both the performance of transmitting the ACK/NACK feedback information, and the utilization ratio of the resources throughout the system.
In summary, in the existing carrier aggregation system, the length of a sequence of ACK/NACK feedback information is determined according to the number of configured component carriers, and if aggregation of at most 32 carriers is supported by the system, then there may be such a large amount of redundant information in the sequence of feedback information in the prior art that may consume higher transmit power and more physical resources, thus degrading the transmission performance and degrading the utilization ratio of the resources.